The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.
Conveyors are used in many industries to convey material from one location to another for various purposes. Most conveyors employ a conveyor belt that moves over rotatable rollers (or idlers). The rotatable rollers are supported beneath the conveyor belt. The conveyor belt moves over the rotatable rollers, with the underside of the conveyor belt contacting the rollers. The upper side of the Conveyor belt carries the material being conveyed.
By way of example, in the mining industry such conveyors may be used to carry ore or other material around a site, from site to site, as well as to loading bays and on to ships, trains, trucks and/or other suitable transportation.
The rollers are held in supports mounted beneath the conveyor belt. These rollers, in turn, support the load of the material conveyed on the conveyor belt. For example, the belts in iron ore mining industries carry very large loads, up to 10,000 tonnes per hour; therefore these rollers are under constant heavy load.
Conveyors also have return rollers which support the conveyor belt on its return journey.
Over time rollers fail for multiple different reasons. In some instances the bearings seize, the roller disintegrates, or can even explodes due to the pressure and heat generated by the roller. Whilst rollers are systematically checked and changed out, roller failure is difficult to predict. As such, rollers can fail whilst in service. These failures can cause hundreds of thousands of dollars worth of damage, as well as loss of production due to the downtime required to effect repairs and/or replacement of broken rollers.
The mining companies typically have full time maintenance crews to maintain the integrity of the conveyors, with some crews repairing the belts and cleaning the scrapers on the belts whilst other crews constantly change out damaged rollers.
Currently, the roller frames which support the rollers are largely formed from a series of channels, referred to in the industry as “RSJ”, and are of rigid construction. They are built to carry three or four rollers of differing length and diameter depending on the conveyor belt size and the amount of material required to be carried on the conveyor belt. The roller frames are attached to stringers which run the full length of the conveyor, and are themselves supported on support frames.
If a roller is damaged during operation of the conveyor it needs to be replaced before it damages the belt. To change a damaged roller a four man crew is typically used. Before the change out can occur the conveyor belt must be cleared of all ore or any other material being carried on the conveyor belt. The time taken to do this depends on the length of the conveyor but can be between 20-90 minutes. Once cleared the crew then use a car jack attached to a makeshift extendable pipe. This is supported on the stringer to push the conveyor belt away from the rollers. Once the belt is pushed away the roller requiring change out is accessible. With this technique the belt can only be pushed away from the roller a sufficient distant to access only one roller. As a result the process needs to be repeated for each roller, and will need to be executed on the other side of the conveyor belt for rollers on that side.
Once the damaged roller has been changed, the conveyor the belt is recharged with ore. This could take a similar period of time to get the ore flowing as it was to clear the belt. Typically the time it takes to actually replace the damaged roller is one hour. Whilst roller change out is scheduled accordingly to maintenance schedules, there are still three to five roller change outs required per week which are unscheduled. This represents a significant down time, even more so if the belt has not been damaged by the failed roller.
Due to the environment in which many conveyors operate, the rollers tend to be quite large and tend to jam in the roller frames. To remove these from the roller frame the maintenance crew typically use a sledgehammer and/or jimmy bars to remove the roller. If the belt has not been or cannot be moved sufficiently clear of the roller then removal of the roller becomes more difficult.
Typically the maintenance crew are required to sit between the return belt and the raised belt in order to access and be able to lift the roller to be changed.
To change the return rollers, a first spread bar is placed on top of the return travel section of the conveyor belt and another spreader bar is placed under the bottom of the return travel section of the conveyor belt. These spreader bars are then linked to each other with a chain block or “come-a-long” at either side of the conveyor belt. Then, the return travel section of the conveyor belt is lifted to take the weight of the conveyor belt off the return roller. In some sections, the conveyor belts have inverted V rollers instead of normal longer type return rollers. These inverted V rollers are exposed to a large amount of pressure and weight as they near the conveyor belt heads and the counter weights.
Another difficulty with roller change out is the roller location. In some instances operators are required to get underneath the conveyor or be lifted to a conveyor in order to change a roller.
With the current practice, only one roller can be safely changed out at a time. Several jacks cannot be placed along the stringer and the belt lifted simultaneously by each jack. Due to the increase in tension the belt would experience, the jacks would experience significant compression which would result in failure of the jacks.
It is extremely difficult and very unsafe to change rollers under the current practice. Not only does the conveyor experience significant downtime, but the labour intensive process requires a large team. The practice is also quite dangerous in light of the loads and type of machinery which is being repaired.
It is difficult to find a solution to roller change out which can be applied to a large range of conveyor configurations. Conveyors vary significantly from site to site. Widths of conveyor belts on mining sites range in size from 600 mm to 2.4 meters and the roller frames are manufactured accordingly to fit differing stringers and conveyor belts. At any one mine site, there can be up to six different sizes of roller frames held in stock. If a roller frame is damaged, even only slightly, the whole frame needs to be replaced and the replacement procedure is a cumbersome operation on its own.
The procedure that the maintenance crews use to change rollers is very cumbersome, labour intensive, hazardous and can lead to accidents. This creates an overhead that operators of conveyors must bear. It would be desirable to eliminate, or at least reduce, the exposure to hazards associated with the roller change-outs and also to reduce the costs associated with plant downtime when rollers require replacement, maintenance or repair.
Other solutions have been developed but these have not provided practical solutions. Most of these solutions are at least partly automated whereby a support frame is placed between existing roller frames on a conveyor system. The support frame is then caused to move upward to engage the conveyor belt and then to raise the belt above the roller frames. In order to raise the support frame, screw jacks or hydraulic rams are used. However, as the operation of the screw jacks/hydraulic rams is performed by an operator on either side of the conveyor the ends of the support frame are raised at different speeds. In light of the weight of the belt as well as the support frame, the support frame tends to readily jam as the sides of the support frame are raised at different levels. When this occurs the operators are required to lower the support frame and start again. Another disadvantage of these systems is their weight. The prior art support frames claim to be portable, however, in reality the support frames are heavy and not easily handled by the operators.
Another solution is the use of scissor type lifts. These lifts are particularly cumbersome, are heavy and due to the large number of parts require significant maintenance, particularly when used in the harsh mining environment. Furthermore, these types of lifts are prone to unwinding or otherwise collapsing when in use.